Existentialism is a philosophical approach that rejects the idea that the universe offers any clues about how humanity should live. A simplified understanding of this thought system can be found in Jean-Paul Sartre's often-repeated dictum, "Existence precedes essence." What this means is that the identity of any one person—their essence—cannot be found by examining what other people are like, but only in what that particular person has done. Because no one can claim that his or her actions are "caused" by anyone else, existentialist literature focuses on freedom and responsibility.

Existentialism attained the height of its popularity in France during World War II. While the German army occupied the country, the cluster of philosophers and writers who gathered together to discuss and argue their ideas at the cafes of Paris captured the attention of intellectuals around the world. The oppressive political climate under the Nazis and the need for underground resistance to the invading political force provided the ideal background for Existentialism's focus on individual action and responsibility.

Although the French war-era writers are most frequently associated with Existentialism, its roots began much earlier. Existentialism can be seen as humanity's response to the frightening loneliness that prompted Friedrich Nietzsche to pronounce in the 1880s that "God is dead." Civilization's loss of faith in religious and social order created an understanding of personal responsibility. This led to literary works that reflect the existentialist's loneliness, isolation, and fear of the uncaring universe. Fyodor Dostoevsky's novels, written in the 1860s and 1870s, show existential themes, as do twentieth- century works by Franz Kafka, Ernest Hemingway, James Baldwin, and Nathaniel West. The French existentialists were so influential on writers throughout the world that it is almost impossible to find a contemporary book that does not show some influence of their thought.